The A&E department at the Royal London Hospital in Whitechapel. Photograph: Karen Robinson for the Guardian

The number of patients waiting more than four hours for treatment in accident and emergency departments has almost doubled in the space of a year, the latest statistics reveal.

Figures show 161,422 patients were left waiting over four hours for "major A&E" treatment between April and June 2011 – 91% more than during the same period in 2010.

A broader measure including minor injuries units and walk-in centres was also up 90%, to 165,279.

The increases come despite a slight fall in the number of patients using A&E services, from 3.6 million to 3.58 million, scotching past Department of Health assertions that the longer waits were down to increased pressure on services.

Around 3% of patients (one in 33) using A&E, minor injury units and walk-in centres waited more than four hours, rising to 5.5% (one in 17) of patients in A&E only. A year ago, those figures stood at 1.5% and 2.5% respectively.

NHS Trusts had previously been mandated to ensure no patient waited more than four hours, and were set an "operational" goal of 98% of patients seen within that time. Lansley axed the wider goal and reduced the operational target to 95%.

The Department of Health insisted waiting times were stable: "These figures show that the vast majority of patients, 97%, are still being seen at A&E within four hours. We replaced the old four-hour A&E target because doctors said it was not in patients' best interest.

"For the first time, we are measuring the overall quality of care in A&E, as well as the time spent in A&E, which allows doctors to decide what is best for their patients. These figures confirm that, through this change, waiting times remain low and stable."

But the latest statistics seem to show an acceleration of the worsening trend in A&E waits. The previous set of NHS data, released in April, showed a 63% year-on-year rise in patients waiting four hours for treatment. The quarter before was roughly the same level, with long waits up 67% on 12 months earlier.. The latest figures show 91% more four-hour plus wait times than a year before.

The trend mirrors growing waiting times across the NHS. Figures released last month showed the number of patients waiting more than 18 weeks for treatment – a target enshrined in the NHS constitution – had increased 33.5% year-on-year, with 27,834 patients waiting longer than that in May alone.

This came despite a pledge from David Cameron that the 18-week target would be retained.

Figures released on Monday regarding waits for diagnostic treatments such as MRI scans and colonoscopies showed an even stronger trend.

In June, more than 12,521 people waited more than six weeks for key diagnostic tests, more than three times the 3,510 left waiting that long a year before.

The number of patients waiting more than three months for diagnostic procedures rose still further, up nine-fold year-on-year, to 1,763 from 190.

However, the total number of diagnosis procedures carried out was up year-on-year, hitting 1.37m in June 2011, 5% more than the same month a year before.